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Session 89 - Starburst Galaxies.
Oral session, Wednesday, January 15
We present single-dish monitoring observations and a VLBA map of the 22 GHz H_2O megamaser emission from the LINER nucleus of NGC 1052. H_2O megamasers are associated with active galaxies and are typically composed of many narrow (\sim a few km s^-1 FWHM) emission features, but the profile of the H_2O emission from NGC 1052 is broad (\sim 80 km s^-1 FWHM) with no evidence for narrow peaks. Currently, one other source (TXFS 2226-184) is known to have an H_2O profile similar to that of NGC 1052. These are the only elliptical galaxies with detected H_2O sources.
Using single-dish telescopes, we have periodically observed the maser in NGC 1052 for nearly 2 years. The velocity centroid of the broad feature has drifted \sim 50 km s^-1 redward during this time. Velocity drifts of the narrow H_2O maser features in the active galaxy NGC 4258 (and perhaps NGC 2639) have been ascribed to orbital motions of gas in a nuclear molecular disk, and it has been unclear whether the changing H_2O profile in NGC 1052 has a similar dynamical origin. Our VLBA map of the nuclear 22 GHz continuum and H_2O maser features shows that the masers are aligned along the same axis as the continuum jet, hence the masers may not be associated with a nuclear accretion disk. The masers are found primarily in two clumps separated by 0.03 pc (0.4 mas), assuming a distance of 17.8 Mpc. The mean line-of-sight velocity between the clumps differs by \sim 50 km s^-1. The velocity ``drift'' detected in the single-dish spectra may thus be caused by variations in the relative strengths of these two maser clumps.
Program listing for Wednesday